Please read our Common HTML pitfalls guide here, as it explains why you see the exact error you are getting: https://itch.io/docs/creators/html5#common-pitfalls
Using aboslute paths instead of relative paths — Your project is hosted on a subdirectory on our HTML5 CDN. If you use an absolute path in your sourcecode then the file your are trying to reference will not be found. This is commonly associated with a net::ERR_ABORTED 403 error in Chrome. Absolute paths are paths that start with a /. Try using relative paths instead.